The present invention relates to an adjustment joint for adjusting position. The invention also relates to fastening elements for fastening objects and setting positions. In addition, the invention relates to a method for installation and position setting using an adjustment joint.
It is known to use permanent and semipermanent radio links in order to facilitate a typically bi-directional radio connection. Radio links relay telephone and data traffic as well as radio and TV signals between stations. The radio link is realized by means of electromagnetic radiation, i.e. radio waves, and the frequency of radio waves in a radio link may range from the RF wave band to the microwave region. Links may be 40 to 50 km long, in which case the link masts are typically 40 to 60 meters tall. Link antennas attached to the masts may be parabolic antennas, for example. Typically, there is a line-of-sight path between the radio link antennas so that radio wave propagation is free.
A known wireless transmission system for telephone and data traffic is the cellular-based public land mobile network (PLMN), such as GSM network, which facilitates wireless communication between a mobile station (MS), such as a mobile phone, and fixed parts of the system while the user of the mobile station moves in the system""s operating area. The radio links between the fixed parts of the system are typically a few kilometers or even shorter, whereby the types and sizes of the antennas used may vary. They may be e.g. antennas attached to masts or walls of buildings that are aimed at their targets, say at an antenna attached to another mast. As a general rule, cell sizes are becoming smaller, which will partly result in a growing number of radio links and, hence, more antenna installations and modifications.
Antennas are used to transmit and receive radio waves. An antenna does not radiate in the same way in all directions but its characteristics may be represented by a radiation pattern which describes the correlation between e.g. the field strength radiated by the antenna and the direction. Indeed many antennas radiate strongly in one direction only, whereby the radiation pattern of such an antenna usually has one main lobe and, in addition to that, weaker side lobes. The radiation pattern is an important factor in antenna design, and radio link antennas are normally very directional, i.e. the direction of the main lobe is both vertically and horizontally narrow. It is then obvious that such an antenna has to be aimed at another, receiving, antenna carefully and with adequate precision.
In the prior art, the aiming of a radio link antenna, for example, has been carried out in such a manner that the field strength of the antenna is measured with a so-called AGC voltmeter. Naturally the measurement has to take place at the target, say at the other end of the radio link, at which the antenna is aimed, and advantageously at the location in which the other antenna is to be, or has already been, mounted. Aiming is carried out in such a manner that first the antenna is pointed to the rough direction of its target, using e.g. a compass, after which the antenna is mechanically turned using its fastening or adjustment means, such as adjustment screws. At the same time the field strength is measured with the voltmeter, and by mechanically turning the antenna one attempts to find the field strength maximum both vertically and horizontally. Thus the main lobe of the antenna is aimed at its target and the antenna can be locked in its position.
Antenna fastening elements typically comprise several lockings, joints and lockable adjustment rods and similar elements for performing in addition to the actual fastening, coarse and fine adjustment in conjunction with the aiming. There are several work stages and typically several screws have to be removed and screwed back on in connection with the aiming. A joint used with the fastening elements typically comprises two joint portions that can be rotated with respect to each other and that are locked in their places by tightening a bolt functioning as an axle. Such a joint is suitable only for coarse adjustment. It may also be that there are no adjustment elements and joints as mentioned above, in which case the antenna must be aimed at its target simultaneously with the fastening, in conjunction with the installation. Typically, antennas are heavy, about 5 to 10 kg, so the fastening elements and adjustment elements tend to be large and difficult to handle.
With decreasing cell sizes also the radio link antenna sizes are becoming smaller and the antennas may typically weigh about 3 kg. Current fastening elements are rather unsuitable for small antennas e.g. because they do not have a sufficient adjustment range, they are very difficult to use for fine adjustment, and they are too large to be inconspicuously installed in urban surroundings. The adjustment range of known fastening elements is typically xc2x125-45xc2x0 in the vertical plane and up to xc2x1180xc2x0 in the horizontal plane.
An object of the present invention is to eliminate the aforementioned problems of the prior art and to provide an adjustment joint with a wide adjustment range for the purpose of aiming, for example. In particular, it is an object of the invention to provide an adjustment joint such that the adjustment joint can be switched from a coarse adjustment mode, fine adjustment mode or locking mode to another one of these modes in a very simple manner just by tightening or loosening the locking means of the adjustment joint, which makes both the installation and the structure of the fastening elements considerably simpler.
A considerable advantage of the invention is that when aiming an antenna one has to tighten or loosen only one locking mechanism fitted to the adjustment joint. Another advantage of the invention is that by means of two adjustment joints according to the invention the aiming can be carried out for a wide adjustment range in both the horizontal and vertical plane.
The invention is used to make the aiming of antennas significantly more accurate, quicker and simpler than in the prior art. A special advantage of the invention is the wide adjustment range, advantageously 180xc2x0 in the vertical plane and 360xc2x0 in the horizontal plane. Another special advantage of the invention is the adequate adjustment range for fine adjustment, advantageously about 10xc2x0, as well as the adequate aiming accuracy, advantageously about xc2x10.25xc2x0, facilitated by the structure. A further advantage of the invention is the small size, whereby a fastening element according to a preferred embodiment of the invention weighs about 2 kg.